The present invention relates to a portable communication device including a function of conducting communication with an external device in a non-contact manner by electromagnetic induction, a reader/writer device, and a resonant frequency adjustment method in the devices.
Nowadays a non-contact communication system in which non-contact IC (Integrated Circuit) cards, such as a traffic ticket and electronic money, are used becomes significantly widespread. In such a non-contact communication system, a transmission signal (electromagnetic wave) emitted from a transmission antenna (a resonant circuit) of a reader/writer (hereinafter abbreviated to as R/W) device dedicated to the system is received by the electromagnetic induction using a reception antenna provided in the non-contact IC card.
In the non-contact communication system, a resonant frequency of the reception antenna of the non-contact IC card or the transmission antenna of the R/W device changes by surrounding environments, such as temperature, humidity, and a peripheral device. In this case, it is difficult to stably transmit and receive information between the non-contact IC card and the R/W device.
Therefore, conventionally there are proposed various technologies for adjusting a deviation of the resonant frequency in the non-contact communication system (for example, see Patent Literatures 1 and 2).
Patent Literature 1 proposes a technique of adjusting the deviation of the resonant frequency (a received resonant frequency) of the non-contact IC card. Specifically, the R/W device transmits a signal to the non-contact IC card while sweeping a transmission frequency (changing a time), thereby detecting the deviation of the resonant frequency of the non-contact IC card. The non-contact IC card acquires the detection result from the R/W device, and adjusts the own resonant frequency based on the detection result.
Patent Literature 2 proposes a technique of mainly adjusting the deviation of the resonant frequency (a transmission resonant frequency) of the R/W device (a wireless communication device). Specifically, a resonant frequency adjusting electromagnetic wave is transmitted from the antenna, and a transmission electric power is detected in the transmission circuit at that time. The detected transmission electric power is compared to a predetermined threshold to adjust the resonant frequency.
Conventionally there are also developed portable communication devices, such as a mobile communication terminal, which include both the same function (hereinafter referred to as an IC card function) as the non-contact IC card and the same function (hereinafter referred to as an R/W function) as the R/W device.